


A Cave Under the Mountain

by LuN4T3



Category: Undertale (Video Game)
Genre: AAAAAAAAAAAA, Alternate Universe - Merpeople, F/F, How Do I Tag
Language: English
Status: In-Progress
Published: 2020-06-30
Updated: 2020-07-01
Packaged: 2021-03-04 07:36:10
Rating: General Audiences
Warnings: Creator Chose Not To Use Archive Warnings, No Archive Warnings Apply
Chapters: 2
Words: 524
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/24999949
Author URL: https://archiveofourown.org/users/LuN4T3/pseuds/LuN4T3
Summary: A long time ago, there was a war between humans and monsters - and ended with human’s victory. Monsters were forced to flee under the mountain, which humans sealed every entrance of it to prevent monsters from being free. However, the cave under the mountain was full of water. . .
Relationships: Alphys/Undyne (Undertale)
Kudos: 3





	1. This Is Our Life Now, Isn’t It?

**Author's Note:**

> Hoi! I’m just trying this website and my own idea of mermonster AU- more like a What IF story, though. 
> 
> Anyway, here goes nothing!

  
It seemed like the war was destined for the monsters to lose, if one were to think about it for some time. Welp, you can’t undo what happened in the past, so why bother to think about it anyway?

  
Monsters didn’t went extinct because of it, and the natural cave under the mountain is quite big. Big enough to have at least three times the monster population. It wasn’t that bad!

  
  
The problem was, the cave is full of WATER.

Since then, monsters were forced to adapt to their new home. It was lucky that they were beings of magic. Or else, they would surely be dead.

As time goes by, monsters started to evolve. The ones with less solid forms were the first to change. They grew fins, gills, or changed to other forms that resembled the organism living in the ocean. The ones with solid forms, however, didn’t change that much except the exchange of body parts; such as having tails instead of legs.

However, monsters weren’t the only ones that changed. The cave itself was also greatly impacted by the excess magic from monsters. The “sky” of the cave grew tiny gemstones that shine like stars, and the water became nearly transparent; as if it is a denser air instead of water.

The areas were mostly distinguished by temperature, mostly monsters with furs were settled in Cold Water as the others decided to settle down at Crystal Cave, Hot Water, Core, and later, New Home.

All in all, life wasn’t so bad for monsters. Hope was still there. 


	2. The Ruins

**Notes for the Chapter:**

> * TW: Briefly mentioned Drowning. *

Today was just an ordinary day for Flowey the (Sea) Flower. Which, lead to boredom pretty soon. The little crown fishes swimming around him were becoming more annoying than entertaining. And for some reason, he just couldn’t LOAD, or RESET as if someone took control over the power!

Flowey pouted at the bottom, occasionally throwing crystals at the fishes that were swimming around him. What a horrible, horrible day.

Then, there was a loud splash. 

~~~~~~

Toriel, the Caretaker of the Ruins, sighed as she glanced up above. A lot of time had passed since the last diver’s visit. She was happy to not lose another child to the cruel King, but she was also lonely. So, so lonely. 

Suddenly, she had a feeling that something changed. For good or not, however, she couldn’t tell. Swimming toward the garden below the Surface, she saw a young diver struggling to get away from a sea flower.

How dare that monster hurting a child! She thought, and hurried to save them. Flinging the anemone to who knows where.

It seemed that their diving equipment was damaged during the FIGHT, making it harder and harder for them to get enough air. 

Horrified, Toriel darted toward them, planting a kiss right next to their lips so they could breath underwater.

Seeing the other’s awe filled face, she couldn’t help but smile as she gently lead them to her house. 

Later, she had her dear friend promise to protect the lost young diver. She knew she couldn’t keep them with her forever. No matter how much she wanted to.

**Notes for the Chapter:**

> Man, I really should come up with a proper name with my AU. Or just good names for each areas. 
> 
> Any suggestions? Please?


End file.
